Accompanying Structural Transformations in Polarity Switching of Heavily Doped Conjugated Polymers

Despite significant recent advancements in highly functional organic semiconductors (OSCs), the n ‐type OSCs reported to date lag behind their p ‐type counterparts in terms of long‐term environmental stability. As an alternative approach to n ‐type materials, a few p ‐type polymers have been shown to undergo dramatic transitions in their charge carrier polarity to n ‐type through transition metal‐incorporated Lewis acid doping. Although the concept of polarity switching is promising, its unclear chemical origin—particularly from a materials science perspective—limits its potential as an n ‐type counterpart. In this work, the chemical and structural mechanisms underlying the p ‐to‐ n polarity switching in a heavily doped conjugated polymer are elucidated. Using gold(III) chloride‐doped indacenodithiophene‐co‐benzothiadiazole (IDTBT) as a model system, doping‐induced thin‐film structural changes are investigated. Quantitative X‐ray photoelectron spectroscopy analysis of doped IDTBT films provides direct evidence of oxidation state changes in Au and Cl ions and confirms the covalent chlorination of the polymer backbone, establishing a direct correlation between the chemical doping mechanism and polarity switching. Finally, leveraging this polarity switching behavior, a p‐n homojunction organic diode is demonstrated with a rectification ratio of 10 ⁴ –10 ⁵ , highlighting the versatility and potential of this excessively p ‐doped n ‐type OSC system for tailoring charge transport properties.